Selective heating apparatus

ABSTRACT

1,039,790. Soldering. INTERNATIONAL BUSINESS MACHINES CORPORATION. July 2, 1963 [July 2, 1962], No. 26119/63. Heading B3R. An apparatus for making one or more solder connections between solder coated bodies, comprises a means for directing heat in a path of thin linear cross-section on to the line of juncture of the bodies. A module 10, Fig. 1, having pre-soldered connections 11 is to be joined to a base 12 having complementary connections (not shown). The apparatus comprises an arm 13 carrying one or more plates 15 of tungsten alumina or beryllium oxide heated by a supporting serpentine element 41 and a pair of locating claws 17, the plates and arms having limited movement in a vertical plane which is restrained when a handle-operated cam 19, 21 is out of engagement with a spring 18. The claws can be engaged with the module when the cam is vertical and in the position shown are released, for example at the end of each heating cycle. The arm 13 may move simply in a vertical plane, or may also have a lateral or swinging movement to obtain modules from a remote location and set them in the required position.

BSO QJ 5i? ma 392835124 1 NOV. 1, .v... R. J. nAwEcm 3,283,124

SELECTIVE HEATING APPARATUS Original Filed July 2, 1962 M VH/Mfi RICHARDJ. KAWECKI United States Patent 3,283,124 SELECTIVE HEATING APPARATUSRichard .I. Kawecki, Endicott, N.Y., assignor to International BusinessMachines Corporation, New York, N.Y., a corporation of New York Originalapplication July 2, 1962, Ser. No. 206,775, now Patent No. 3,230,333,dated Jan. 13, 1966. Divided and this application May 7, 1965, Ser. No.470,335

Claims. (Cl. 219-447) This is a division of application Serial Number206,775 filed July 2, 1962 and now Patent Number 3,230,338 issuedJanuary 18, 1966.

The invention relates broadly to selective heating apparatus, and inparticular to apparatus for providing restricted area heating to effectconnections of electronic and electrical components, andcomponent-carrying modules arranged in miorominiature packages.

The present direction of developments in the area of electrical andelectronic packaging is toward the use of extremely small components ina very closely spaced arrangement providing total units of highcomponent density. Further, components are arranged to form modularstructures having fixed circuit relations within the modules and whereelectrical connections to external circuitry are provided by spacedlands on outer surface portions. A complete modular circuit package mayinclude a number of such modules arranged on a common interconnectionsurface, and it is with this latter general class of modular packagingarrangements that the present invention is contemplated as beingespecially useful.

Electrical connections in such modular circuits pose a difficult problemmainly because of the relatively small size of the modules and the largenumber of connections to be made to an individual module. For example,one such known module is approximately .300 x .300 x .020 inch andrequires as many as seven electnical connections to be made along asingle edge. It is clear that making these connections by the use ofconventional soldering devices would not be a feasible process.

It is therefore a primary object of the invention to provide anapparatus for directing heat onto relatively small, sharply definedareas.

A further object of the invention is the provision of such an apparatuswherein a plurality of points arranged in a line are heatedsubstantially simultaneously.

A further object of the invention is the provision of such an apparatusin which heat is simultaneously applied to pretinned areas to effectreflow soldering.

A still further object of the invention is the provision of such anapparatus in which heat in radiant energy form is directed in a formedbeam onto a plurality of areas at which points solder reflow is to beeffected.

Yet another object of the invention is the provision of a radiant energylineal heating means in which surface tension forces of molten solderserves to bring a workpiece into registry with mating interconnectionareas on a mounting means.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings.

In the drawings:

FIGURE 1 is a perspective view of an embodiment for practicing theinvention;

FIGURE 2 is an elevation sectional view of a special heat directing andforming means for the embodiment of FIGURE 1; and

FIGURE 3 is a more detailed elevation view of the lens shown in FIGURE2.

With reference now particularly to FIGURE 1 and the embodiment of theinvention illustrated therein, it is important to note first of all thatalthough the invention is considered to have applicability to other anddifferent types of workpieces, it will be described here in relation toeffecting solder reflow electrical connections on a circuit modularpackage 10 in which regard it has been found to be especially useful.This package comprises a generally rectangular circuit base includingelectronic and/ or electrical components mounted thereon and having aplurality of individual connection points 11 arranged along a pair ofopposite edges in a spaced lineal manner. And it is a main purpose andfunction of the invention to direct heat onto these edge connectionpoints and mating lands of an interconnection board 12 in registrytherewith to effect solder reflow between respective points and lands.It is also contemplated that the modules 10 are relatively small, forexample in the neighborhood of .300 of an inch square and of a thicknessof 020-.050 inch, and that a plurality of such modules can beinterconnected to form a so-called mierominiature circuit or machine.

When effecting either solder reflow or conventional soldering, it isclear that excessive amounts of heat can quickly and easily damage themodules themselves, or the components carried thereby or burn offinterconnection points and associated lands causing failure of thepackage. Further, because of the relatively small size of the solderingareas and the multiplicity of such areas in a small space, conventionalsoldering apparatus would be highly ineffectual and time consuming for afeasible production process.

The embodiment of the invention illustrated in FIG- URE 1 is one inwhich the heating means, according to the invention, is effectuate-d byinfra-red energy. More particularly, there is provided a specialincandescent lamp 42 which provides an infra-red light beam. A concavereflector 43 is arranged in a semi-surrounding relationship to the heatsource 4-2 for directing energy from the source along a path towards aspecial focusing means 44;. The focusing means is enclosed in asimilarly shaped back reflecting means 45 having surfaces facing in thegeneral direction towards the source 42, but especially arranged so thatsuch back reflection does not gene-rally impinge on the source. Thislatter feature is important in that it increases the operational life ofthe source 42.

A small slit is provided in the reflector 45 for receiving similarlydimensioned portions of the focusing means 44 theret'hrowgh such that anarrow lineal element of concentrated infra-red energy is passed throughthe slit and focused onto the junction of the module v10 and themounting board 12. Thus, whereas in my aforementioned patent the heatingmember was brought into physical contact with a portion of the linealarea at which heat was desired to be supplied, in this embodiment of thepresent application radiant energy is focused onto the line.

Certain specific constructional features of the focusing member 44 areof importance here. As shown best in FIGURE 2, when viewed along an edgelooking at right angles to the direction of light propagation, it has agenerally isosceles triangle shape where the incident energy impinges onthe base and emerges generally at the opposite angle. Also, the edgealong which light energy emerges is extended somewhat in the directionof light propagation to provide a pair of surfaces 46 substantiallyparallel to one another with the extremity being rounded off into agenerally semi-cylindrical termination. It is this slight extension withthe parallel sides which is received through the slit in the backreflector for focusing the infra-red energy in the desired manner. Moreparticularly, light coming from the source 42 passes through the flatsurface of the focusing means 44 for refraction at the curved end into athin lineal element, and extraneous light is reflected backwardly andaway from the source 42. As shown in greater detail in FIGURE 3, thelens 44 comprises three portions indicated generally by the referencenumerals 43, 49, 50. Portion 48 is in the shape of a truncated trianglehaving a base 51 at one end and converging sides 47. Adjacent to theopposite or truncated end of portion 48 is an intermediary portion 49having a generally rectangular shape and two parallel sides 46 whichextend from the converging sides 47 as aforementioned. The body 44 isterminated in a third portion 50 which has a face 52 of a predeterminedcurvilinear shape which is illustrated as semi-cylindrical. Thus, as isshown in FIGURE 3, some of the energy from the lamp 42 is focused by theface 52 into the aforementioned concentrated image or line which appearsin cross section as the circle 53 in FIGURE 3. On the other hand, someof the energy is diffused by the parallel sides 46 and face 52 into twoadjacent side images, represented in cross section as circles 54, 55 inFIGURE 3. For purposes of illustration, the dash lines 56 represent theray traces of some of the energy which produces the two adjacent sideimages 54, 55 and the dash-dot lines 57 represent the ray traces of someof the energy which produces the center image 53. For sake of clarity,only that part of the ray traces 57 emanating from the lens 44 areillustrated. Due to the configuration of the lens 44, the latterinherently provides a zone of less intensified thermal energy whichsurrounds the main image 53 and thereby provides a more uniform thermaldistribution in the workpieces which are to be joined. Moreparticularly, the main image is focused on the actual pretinned solderedor pretinned parts of the workpieces and the side images are disposed onthe adjacent non-soldered parts. As a result, the temperature gradientbetween the actual parts and the adjacent non-soldered parts of theworkpieces is not so pronounced and hence the causes of thermalfractures is thereby mitigated. In actual use, the exact amounts ofenergy required and the duration of heating will have to be determinedfor each particular type of application; however, specifics in thisregard are considered mainly matters of design.

A further important feature here is the material from which the focusingmeans 44 is constructed. Although, of course, glass can be utilized toperform the function of focusing, it is not satisfactory here due to thehigh concentration of heat, which, even when used for a very short time,has been found to cause cracking in the glass. Or, when resort to hightemperature glasses is made there is a concomitant high degree ofinfra-red absorption which is undesirable. The best material known forthis purpose is salt (NaCl) which has a satisfactory high index ofrefraction, can withstand exceptionally high amounts of heat withoutbecoming distorted or breaking down, and has a high transmissivity toinfra-red. Salt, however, is hygroscopic and unless used inexceptionally dry environments it must be protected from the moisture.This is accomplished there by coating the surface of the means 44 with acoating 47 of a low melting glass material which isolates the saltsurface from moisture bearing atmospheres. An alternative is toaluminize the surface of the means 44 a suflicient amount to protect thesurface, but not so much as to reflect a significant amount of theinfrared.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formand details may be made therein without departing from the spirit andscope of the invention.

What is claimed is:

1. Apparatus for localized area heating of workpieces restinglycontacting one another, at least one of said workpieces having a lowmelting metal coating at the localized area thereof, said apparatuscomprising:

a source of infra-red energy, and

heat directing means including a focusing means adapted to receive theinfra-red energy and provide a concentrated beam of dimensionscommensurate with those of the localized area while obstructingtransmission of infra-red energy outside the beam, said focusing meanscomprising:

a lens system formed from an integral body having a first truncatedtriangular cross-section portion having a base at one end thereof andtwo converging sides, an intermediary second rectangular cross-sectionportion adjacent to the truncated end of said rectangular crosssectionportion of said body and having two opposing parallel sides extendingfrom the two converging sides of said first portion, and a third portionterminating in a face having a predetermined curvilinear shape, saidbody being positioned with respect to said infra-red source such thatthe infrared energy enters the base of the first portion of said bodyand passes through said first, second and third portions of said bodyand emanates from the face of said third portion, some of said infra-redenergy passing through said body being focused by said face into a lineof concentrated thermal intensity and some of said infra-red energypassing through said body being diffused by said second rectangularcrosssectional portion of said body to provide a zone of lesser thermalintensity about said concentrated line, said workpieces being positionedwith respect to the face of said body so that said concentrated line ofthermal intensity lies substantially on the localized area to be heatedto cause the metal coating to reflow and thereby effect the bonding ofsaid workpieces.

2. Apparatus according to claim 1 wherein said heat direct means furthercomprises:

means for enclosing said focusing means, said means for enclosing havingfirst aperture means through which at least the third portion of saidbody protrudes and having a second aperture exposing said base to saidinfra-red source.

3. Apparatus according to claim 1 wherein said lens is comprised ofNaCl.

4. Apparatus as in claim 3, in which the lens is coated with a lighttransmissive material which is non-hygroscopic.

5. Apparatus according to claim 1 wherein said infrared sourcecomprises:

an infrared lamp, and

reflector means positioned with respect to said lamp to reflect saidinfra-red energy toward the base of said body.

References Cited by the Examiner UNITED STATES PATENTS 1,965,865 7/1934Thompson 240-1 X 2,077,102 4/1937 Fardon 240 1 X 2,364,730 12/1944Leskin. 2,561,077 7/1951 Tilton 88-57 X 2,604,005 7/1952 Hahn. 2,945,9587/1960 Morris 881 X FOREIGN PATENTS 752,400 6/1953 Germany.

938,499 2/1956 Germany.

264,814 12/1927 Great Britain.

ANTHONY BARTIS, Primary Examiner.

1. APPARATUS FOR LOCALIZED AREA HEATING OF WORKPIECES RESTINGLYCONTACTING ONE ANOTHER, AT LEAST ONE OF SAID WORKPIECES HAVING A LOWMELTING METAL COATING AT THE LOCALIZED AREA THEREOF, SAID APPARATUSCOMPRISING: A SOURCE OF INFRA-RED ENERGY, AND HEAT DIRECTING MEANSINCLUDING A FOCUSING MEANS ADAPTED TO RECEIVE THE INFRA-RED ENERGY ANDPROVIDE A CONCENTRATED BEAM OF DIMENSIONS COMMENSURATE WITH THOSE OF THELOCALIZED AREA WHILE ABSTRUCTING TRANSMISSION OF INFRA-RED ENERGYOUTSIDE THE BEAM, SAID FOCUSING MEANS COMPRISING: A LENS SYSTEM FORMEDFROM AN INTEGRAL BODY HAVING A FIRST TRUNCATED TRIANGULAR CROSS-SECTIONPORTION HAVING A BASE AT ONE END THEREOF AND TWO CONVERGING SIDES, ANINTERMEDIARY SECOND RECTANGULAR CROSS-SECTION PORTION ADJACENT TO THETRUNCATED END OF SAID RECTANGULAR CROSS-SECTION PORTION OF SAID BODY ANDHAVING TWO OPPOSING PARALLEL SIDES EXTENDING FROM THE TWO CONVERGINGSIDES OF SAID FIRST PORTION, AND A THIRD PORTION TERMINATING IN A FACEHAVING A PREDETERMINED CURVILINEAR SHAPE, SAID BODY BEING POSITIONEDWITH RESPECT TO SAID INFRA-RED SOURCE SUCH THAT THE INFRARED ENERGYENTERS THE BASE OF THE FIRST PORTION OF SAID BODY AND PASSES THROUGHSAID FIRST, SECOND AND THIRD PORTIONS OF SAID BODY AND EMANATES FROM THEFACE OF SAID THIRD PORTION, SOME OF SAID INFRA-RED ENERGY PASSINGTHROUGH SAID BODY BEING FOCUSED BY SAID FACE INTO A LINE OF CONCENTRATEDTHERMAL INTENSITY AND SOME OF SAID INFRA-RED ENERGY PASSING THROUGH SAIDBODY BEING DIFFUSED BY SAID SECOND RECTANGULAR CROSSSECTIONAL PORTION OFSAID BODY TO PROVIDE A ZONE OF LESSER THERMAL INTENSITY ABOUT SAIDCONCENTRATED LINE, SAID WORKPIECES BEING POSITIONERD WITH RESPECT TO THEFACE OF SAID BODY SO THAT SAID CONCENTRATED LINE OF THERMAL INTENSITYLIES SUBSTANTIALLY ON THE LOCALIZED AREA TO BE HEATED TO CAUSE THE METALCOATING TO REFLOW AND THEREBY EFFECT THE BONDING OF SAID WORKPIECES.